Won’t take the first treat

I have a 9-month-old (he's a mini mix of doodles). He's not super food motivated, and I've been told by a trainer that he's incredibly smart. I'm baffled by this behavior:

I do two formal training sessions/day, using half of his kibble for each breakfast and lunch (teaching: sit, down, touch, stay, watch me, heel, leave it, place).

Lately, I will tell him it's training time and then give him his first command. He does it dutifully, but then he won't eat the treat from my hand. I can do a few more commands and he'll do them, but then he'll start to only VERY reluctantly do them, refusing to take any treats. This used to happen rarely, but now I feel like it's happening more frequently. Sometimes, I can get him to eat the treat if I put it on the floor in front of him (though this doesn't really work any more–in part, because he's learned "leave it" and might think I'm testing him). I will offer him the treat and he'll look away, or he'll wriggle around–sometimes pawing at his snout.

BUT HERE's THE THING… once I manage to get him to eat the first treat (by putting it on the floor or being SUPER excited about it [I never force him]), it's like I've broken the seal and he'll eagerly eat more treats and do more commands without any problems. It's getting past that first treat that seems to be the problem.